When the air conditioning in your vehicle is operating, the only sound you should hear is the sound of air blowing out of the vents. Any other type of car A/C noises should be a cause for concern because they indicate either a problem with your A/C or the vehicle in general.
If you hear a noise that sounds like metal grinding on top of the metal, this means that the serpentine belt has become damaged or loose or you’ve got an issue with the compressor. If it’s the compressor, it could be its pistons which are used for compressing refrigerant gas. They will emit the metallic grinding sound once the compressor becomes worn, and you’ll definitely want to replace it.
If it’s the fan belt, the sound comes from the belt rubbing up against various components within the A/c housing. The good news is that, unlike the compressor, a worn or loose fan belt is relatively simple to repair. However, it is absolutely essential to discontinue using the A/C as soon as you hear this noise because if you keep running it, the belt might hit other components which can cause them to malfunction.
A buzzing sound signals that you might have an electrical issue with multiple components, especially the contact relay switch or the condenser’s fan motor. The buzz comes from the electricity hopping between circuitry, and within A/C units, this is usually a sign that it’s reached the end of its service life. And it is not something you want to ignore, because even if the A/C is still cooling down the cabin, not getting it resolved promptly can lead to more damage that will be costlier to repair. Even worse, A/C electrical problems can lead to fires so immediately stop using it if you hear buzzing.
Whistling or Hissing
If you hear a whistling or hissing noise, it could be something as simple as refrigerant gas within the expansion valve, which by itself isn’t a big deal, especially if it only lasts for a few moments. However, a whistling or hissing sound that is persistent could be an indication of refrigerant leakage. These leaks usually happen within the internal valve or refrigerant lines, and you might also hear the sound of bubbling. If the issue isn’t resolved promptly, the leak will intensify as will the noise that it makes. As with buzzing noise, you should immediately deactivate your A/C if you detect a continuous whistling, hissing or bubbling noise and take it to a professional. Otherwise, you or your passengers could end up inhaling Freon which can be hazardous.
The one thing to keep in mind with all these noises is that you should not continue using your vehicle’s A/C once you hear them. Turn off the air conditioning immediately and get the vehicle to a mechanic as soon as possible. While this means you’ll probably have to roll down your windows for a while, especially if you don’t have much cash, not using the A/C will prevent further damage and minimize your repair costs.